1. Field of the Invention
The teachings herein relate to three-dimensional (3D) displays and, in particular, to image enhancement for a 3D display.
2. Description of the Related Art
Optical elements that use spatial de-multiplexing have been used to create 3D images for nearly a century. Exemplary optical elements include narrow vertical slits or lenticular sheets.
The method of spatial de-multiplexing by use of lenticular sheets (i.e., arrays) generates a 3D image from a two-dimensional (2D) image. The resulting 3D image has a lower resolution than that of the 2D image. Reference may be had to FIG. 1.
In a prior art display apparatus 10 depicted in FIG. 1, an image source 2 provides a 2D array of pixels 3. The 2D array of pixels 3 provides information to a single array of lenticular lenses 4 (in some embodiments, the array of lenses is referred to as a “lenticular lens”). The lenticular lenses 4 optically manipulate light from pixels 3 to generate ray information 5 that forms a 3D image wavefront 6.
The 3D wavefront 6 is produced by aligning each lenticule of the array of lenticular lenses 4 so that a field of view for the lenticule covers several pixels in the array of pixels 3. Each pixel that is within the field of view is converted to ray information 5 by the refractive properties of the lens. Thus, each lenticule becomes an emitter with angularly varying intensity components. The geometrical properties of the 3D wavefront 6 can consequently be represented by correct parameterization of spatially and angularly varying components of the ray information 5. In general, the more pixels 3 that can be associated with the lenticular lenses 4, the more accurate the 3D image wavefront becomes. Thus, in the prior art, it is desirable to have a very high resolution image source 2, since this will allow one to produce a 3D image with modest spatial resolution and good ray sampling. However, such display apparatus 10 are not without drawbacks.
For example, such display apparatus 10 typically use cylindrical lens arrays as the lenticular lenses 4. The use of cylindrical lens arrays creates horizontal-parallax-only (HPO) imagery. One particular drawback of using cylindrical lens arrays is that in the common configuration, horizontal resolution and vertical resolution of the image source 2 are not equally reduced by the lenticular lenses, resulting in a 3D image 6 with unequal horizontal and vertical resolution. Reference may be had to FIG. 2.
In FIG. 2A, a portion of the prior art display apparatus is depicted. This illustration shows cylindrical lenticular lenses 4 which are aligned with the image source 2. The alignment of the lenticular lenses 4 is consistent with an orientation of the pixels 3 in the image source 2. That is, as shown in this illustration, the lenticular lenses 4 share a direction (a y-axis direction) with the pixels 3 included in the array. The orientation of the lenticular lenses 4 are further described in FIGS. 2B and 2C. In FIG. 2B, the lenticular lenses 4 are shown according to the x-axis (from the top), and in FIG. 2C, the lenticular lenses 4 are shown according to the y-axis (from the side). As shown in FIGS. 2B and 2C, the image source 2 produces output rays 5 which are focused by the lenticular lenses 4. Whereas the reconstructed 3D image 6 has one reconstructed vertical pixel for each input pixel 3, the reconstructed x resolution is degraded in this illustration by a factor of approximately ⅕.
In FIG. 2, the lenticular lenses 4 are shown as generally cylindrical lenses. As the cylindrical lenses do not have any optical power along their height (the y-axis), they cannot convert pixel information into ray information along this axis (see FIG. 2C). In a typical 3D display, this type of arrangement sacrifices quality of the 3D image along one axis.
In FIG. 3A, an image source 2 provides an array of pixels 3. As shown in the illustration, the pixels 3 are distributed along an x-axis and a y-axis. As is known in the prior art, lenticular lenses are used to provide for focusing of output rays from the image source 2. In this example, the lenticular lenses are tilted lenticular lenses 30.
In this example, the tilted lenticular lenses 30 are tipped slightly with respect to the pixels 3 of the image source 2. This provides an effect such that a respective center of each pixel 3 for each row of pixels 3 is offset slightly from an optical axis 31 of each tilted lenticular lens 30. Since a direction for an output ray 5 from each pixel 3 is proportional to offset from the optical axis 31, adjacent pixels 3 along a column are output in different ray directions. Thus, vertical resolution may be controlled along with the horizontal resolution to achieve greater ray sampling. That is, in practice, an observer will see a multiple of the number of rays (for example, 8 instead of 4) as compared to the system using parallel lenticular lenses. This is shown in FIG. 3D. Although this technique provides for equalization of resolution in the x-axis and the y-axis, output rays 5 from pixels 3 of adjacent rows overlap one another, and thus produce the equivalent of a low-pass filter. Reference may be had to FIGS. 3B, 3C and 3D as well as FIG. 4.
In FIG. 3B, a first row of pixels in the image source 2 is shown. In FIG. 3C, a second row of pixels in the image source 2 is shown. The second row is slightly offset from the first row (that is, effectively offset from the first row), due to the tilting of the lenticular lens 30. Output rays 5 from the combination are shown in FIG. 3D. The x-axis depicted in FIG. 3 shows an alignment of pixels 3 in each row with the pixels in the first row (Row 1).
Various forms of focusing lenses are used. In this example, the tilted lenticular lenses 30 having a desired orientation are generally referred to as “tilted” or “clocked.” The parallel lenticular lenses 4 (which have no angular deflection from a column of pixels) are generally referred to as “parallel” (with reference to a pixel axis) and by other similar terms. It is recognized that lenticular lenses may take on various forms and are not limited to tilted, parallel, cylindrical, elliptical or by other shapes. Each lenticule may be a singlet, doublet, or other lens type.
FIG. 4 shows how providing the tilted lenticular lenses 30 (relative to a prior art cylindrical lenticular lens 4) provides a desired view resolution. Though centers of pixels 3 for pixels 3 in adjacent rows are horizontally offset, the horizontal field of view for these pixels overlap, effectively low-pass filtering the output rays 5 and producing a generally undesirable effect. This results in “view overlap” (interview crosstalk), which has a side effect of limiting the degree of depth in the reconstructed 3D image 6. The resulting view overlap between two pixels in adjacent rows is shown in FIG. 4C.
What are needed are methods and apparatus, such as those disclosed herein, for providing improved resolution in a 3D image, where a vertical resolution and a horizontal resolution (along both axes of a 2D image source) appear to be about equal, and where view overlap is minimized.